Making Things HappenSimple Motor Control

How Your Brain Works - Week 6

Dr. Jan Schnuppjan.schnupp@dpag.ox.ac.uk

HowYourBrainWorks.net

“Efferents and Effectors”• “Efferent” nerves carry impulses “away” from the

central nervous system.• Eventually they have to end either in muscles or

in glands.• Physiologists distinguish 3 types of muscle:

“smooth”, “cardiac” and “striate” (or skeletal”)

Skeletal Muscle

• There are ca 640 skeletal muscles in a human body

Nervous Control of Skeletal Muscle

Motor Cortex

Basal GangliaCerebellum

Spinal Cord

Muscle

Muscle Fibre

Structure

axonsaxons

muscle fibresmuscle fibres

musclemuscle

Organisation of Muscle FibresOrganisation of Muscle Fibres

(actin)

(myosin)

Ca++ exposes Myosin Binding SitesCa++ exposes Myosin Binding Sites

The Myosin CycleThe Myosin Cycle11 22

3344

1.Myosin binds to actin.

2.Myosin head bends backward, releasing ADP and pulling itself forward.

3.ATP binds to myosin, causing release from actin.

4.Myosin uses energy from ATP hydrolysis to stretch itself, ready to undergo new binding and pulling cycle.

Motor Units

Muscle Spindles

The Stretch Reflex

Muscles tend to be arranged in pairs

• Muscles can only contract. • If one muscle bends a limb (the “flexor”) then there must be another

muscle to stretch it (the “extensor”).• Muscles are therefore typically arranged in agonist-antagonist pairs.

Spinal Cord Antagonist

Circuits

Matthews “Neurobiology” Figure 8-3

Postural support through spinal

reflexes

Spinal Pattern Generators

Spinal cord pattern

generators

Headless Chicken

• Warning: some viewers may find the content of this video clip distressing.

Break

Motor Related Areas of Cortex

SomatosensoryCortexSomatosensoryCortexSomatosensoryCortex

Premotor Area

Frontal EyeFields Primary Motor

Cortex

SupplementaryMotor Area

Broca’s Area

Penfield’s Homunculi

The Cortico-spinal Tract

Motion Direction Sensitivity in Monkey Primary Motor Cortex

• Georgopoulos et al, Science 1986

Silicon Array Electrodes

Primate moving robot arm

Human Primate Matthew Nagel

What about “Higher Order” Motor Cortex?

SomatosensoryCortexSomatosensoryCortexSomatosensoryCortex

Premotor Area

Frontal EyeFields Primary Motor

Cortex

SupplementaryMotor Area

Broca’s Area

Mirror Neurons

Broca’s Area

• Broca’s aphasia is usually associated with lesion to the left frontal cortex.

• See here the brain of Broca’s Patient, Mr Leborgne (“TanTan”) features a large lesion in Broca’s area.

Motor Aphasia

Motor Aphasia 2

Wernicke’s Area

• Wernicke’s aphasias are often associated with lesions at the boundary of the superior temporal and parietal lobes on the left hemisphere.

A Patient with Wernicke’s Aphasia

• From the archives of the University of Wisconsin

The Arcuate Fasciculus

Big fibre bundle connecting Broca’s and Wernicke’s Areashttp://www.biocfarm.unibo.it/aunsnc/pictef14.html